1. Field of the Invention
The present invention relates in general to switched mode electronic circuits and in particular to circuits and methods for reducing interference from switched mode circuits.
2. Description of the Related Art
Class D audio power amplifiers (APAS) have been used for many years in systems, such wireline telephony, where high bandwidth is not critical. More recently however, new fabrication techniques, and in particular, new techniques for fabricating power transistors, have made integrated Class D APAs possible. This has extended their potential applications to lower-power, higher-bandwidth systems, including battery-powered portable music players and wireless communications devices.
One major advantage of Class D amplifiers is their efficiency. Generally, an audio signal is converted into a relatively high frequency stream of pulses varying in width with the amplitude of the audio signal. This pulse width modulated (PWM) signal is used to switch a set of power output transistors between cutoff and saturation which results in efficiencies above 90%. In contrast, the typical Class AB push-pull amplifier, using output transistors whose conduction varies linearly during each half-cycle, has an efficiency of around 60%. The increased efficiency of Class D amplifiers in turn reduces power consumption and consequently lowers heat dissipation and improves battery life.
Similarly, switched mode power supplies have found wide acceptance in the design of compact electronic appliances. Among other things, switched mode power supplies advantageously use smaller transformers and are therefore typically more compact and lighter weight. This is in addition to the increased efficiency realized over linear power supplies. Moreover, the total number of components can be reduced to, for example, a power MOSFET die and a PWM controller die packaged together in a single package.
Given the importance of improved battery-life, reduced heat dissipation, and component size minimization in the design and construction of portable electronic appliances, improved switched mode techniques will have numerous practical advantages. The possible applications for these techniques are numerous, although Class D APAs and switched mode power supplies are two primary areas which should be considered.